This invention relates to magnetron microwave sources, and, more particularly, to a magnetron microwave source having an antenna covered by an output dome.
Microwaves are radio frequency energy used in a wide variety of commercial and military systems. Microwaves have frequencies in the range of from about 0.9 to about 100 GHz (gigahertz). Their applications include, for example, microwave ovens, microwave radar, microwave communications, and materials deposition.
Microwaves may be generated in any of a variety of microwave source systems. A typical magnetron microwave source system, for example, includes a cylindrical cathode and a surrounding anode having inwardly extending vanes that define a series of resonant cavities. A magnetic field is applied parallel to the cylindrical axis by strong magnets located at the ends of the cathode and anode. A microwave antenna is provided at one end of the structure in communication with the anode. The microwave source system is enclosed in a housing so that it may be evacuated.
In operation, electrons are emitted from the cathode into the space between the cathode and the anode and accelerated toward the anode by an applied electric field. The electrons are forced to move in an expanding circular orbit about the cathode by the simultaneously applied magnetic field. As the electrons pass by the resonant cavities, they generate a continuously oscillating electromagnetic field. The frequency of the electromagnetic field is determined by the configuration of the resonant cavities. The electromagnetic energy is conducted into the antenna, from which it is radiated into a launcher and thence into a waveguide output transmission line. A wide variety of magnetron and other types of microwave sources are known. The above discussion is for general background purposes, and is not intended to be exhaustive or detailed.
The microwave antenna is covered with an output dome made of a ceramic material such as aluminum oxide (alumina). The ceramic output dome forms part of the vacuum enclosure that permits the cathode, anode, and related structure to be evacuated. Because the output dome has a low electrical conductivity and low electrical loss factor, it permits the passage therethrough of the microwave energy that is radiated from the microwave antenna.
The ceramic output dome may be a limiting consideration in the output power of the microwave source system. In some high-average-power applications, the ceramic output dome is observed to crack from the influence of the absorbed microwave energy. The vacuum is thereby lost and the microwave source system becomes inoperable.
There is a need for an improved microwave source system which does not suffer from loss of function as a result of ceramic output dome failures. The present invention fulfills this need, and further provides related advantages.